Network establishment and management protocol

ABSTRACT

The invention relates to a protocol for communications between networked devices. The devices are logically arranged as a hierarchy of device types including a controller device type (52) from which no other device type depends and a basic device type ( 54 ) from which a number of other device types depend. The devices implement a simple device description message of fixed length and format which includes the device type, and some devices further implement an extended device description message including additional information.

This invention relates to a network protocol, and in particular to implementations of the protocol.

A prior art protocol for network management is universal plug and play (UPnP), which is very useful for internet applications where bandwidth, battery consumption, and to an extent cost, are not an issue. Implementations of the protocol in consumer electronics (CE) do exist, but because of the extent of the protocol, such implementations impose a heavy load especially on the simplest devices that otherwise would require only minimal processing capability.

The need therefore exists for a protocol suitable for embedding in simple devices such as lights, thermostats and CE equipment (remote control for TV's, DVD's and PVR's), that is simple and cost effective to implement, requires the minimum of bandwidth, yet is scalable across a range of devices with varying capabilities.

This need is not restricted to wireless application, but extends to wired applications.

According to a first aspect of the invention there is provided a method of operating a networked device, including: receiving token-compressed messages; recognising in the received token-compressed messages incoming simple device description query messages requiring a simple device description response from the networked device, without decompressing the incoming messages; and sending a simple device description including a device type as a response to an incoming device query message requiring a simple device description response.

Such a method implements the protocol that is the subject of this patent application. The protocol itself will be referred to as home uniform control language (HUCL).

The ability for simple devices to be able to operate directly on compressed token-coded messages allows for simple devices to be able to be made without excessive hardware or software requirements. More complex devices can decompress the messages and operate on them in more complex ways. Thus, the approach according to the invention allows simple devices to be combined with complex devices in an integrated network without difficulty and allowing the full functionality of complex devices without overloading simple devices. Simple devices may simply ignore extended device description queries.

The Simple Device Description includes a small or moderate number of predetermined fields each field being of fixed length. In general, the same fields will be used for each message, although there may be some variation. For example, a composite device may include an additional integer field including the number of sub-devices as explained below.

The simple device description message is in the form of a token-compressed message compressed from a human-readable message format. Preferably, the message includes a device type value representing the type of the other device; the device type value being selected from a device type hierarchy having predetermined top level elements including a controller device type and a basic device type, and at least one further level of subsidiary device types depending from the basic device type and inheriting properties of higher level device types on which the subsidiary device type depends, but not including any further level of subsidiary device types depending from the controller device type.

According to the HUCL protocol, the underlying message format is a human readable format, such as XML. However, to save bandwidth, messages are passed between networked devices in compressed form. A networked device is nevertheless able to process such compressed messages, because the compression method used is token compression, which replaces common strings with tokens. The networked device can thus recognise the compressed tokens without decompression, at least enough to recognise a query requiring a response of a simple device description, and then respond with a simple device description. Thus, a networked device can be implemented with little overhead.

A suitable form of token coding is described in “wap binary XML content format” of 24 Jun. 1999, available at http://www.w3.org/TR/wbxml.

It will be noted that although there is at least one hierarchy depending from a basic device type, i.e. a hierarchy of controlled devices, there is no corresponding hierarchy of controller devices. This is to keep the simple device description messages as short and simple as possible—many controllers, such as a universal remote control, are capable of controlling a number of different device types.

The invention, in a second aspect, relates to a networked device, comprising: a transceiver for sending and receiving token-compressed human readable messages; and a message handler arranged to carry out the steps on incoming token-compressed human readable messages of: recognising received device query messages requiring a simple device description response from the networked device, without decompressing the incoming messages; and sending through the transceiver a simple device description including a device type as a response to an incoming device query message requiring a simple device description response.

The networked device may further include a predetermined simple device description message precompressed from human readable format, wherein the message handler is arranged to read the predetermined simple device description message from the memory and send it through the transceiver in response to an incoming device query message.

In a further aspect, the invention relates to a system, comprising:

a plurality of networked devices each having a transceiver for sending and receiving network messages; at least one networked device arranged to send a simple device query message to other devices and to receive and interpret simple device description messages subsequently received from the other devices; each of the networked devices being arranged to respond to an incoming simple device query message from another of the devices by sending a simple device description message of defined length including a device type value representing the type of the device; and wherein the plurality of networked devices include at least one simple device without the capability to decompress messages and interpreting directly compressed messages and at least one complex device including a message decompression arrangement for decompressing the messages and a message interpreter for interpreting the decompressed messages.

For a better understanding of the invention, embodiments will now be described purely by way of example, with reference to the accompanying drawings in which:

FIG. 1 shows a system including pair of devices according to an embodiment of the invention;

FIG. 2 shows a schematic of the software in one device;

FIG. 3 is a flow diagram of the device discovery process;

FIG. 4 is a schematic of the device type hierarchy;

FIG. 5 shows the steps that a controller carries out to inform a controlled device of its control capability of that device;

FIG. 6 shows the steps that a controller carriers out to determine its control capability of a controlled device;

FIG. 7 shows the structure of the software;

FIG. 8 illustrates the HUCL protocol; and

FIG. 9 illustrates a simple device description message.

The protocol HUCL is a lightweight, low bandwidth control protocol primarily designed for wireless systems. The messaging format is based on XML, and messages are compressed prior to transmission. The use of XML provides an extensible and scalable solution with the compression reducing the data sent, so reducing the amount of time the transmitter is on and consuming power.

The general principles of the HUCL protocol and how it would operate on a device will now be discussed with reference to a simple example.

Referring to FIG. 1, a light switch 2 and a light fitting 4 are provided, the latter being an embodiment of the invention. The light switch 2 has a physical rocker switch 6 operated by the user, together with an RF transceiver 8 and battery 10, together with control circuitry 12 and memory 14. The light fitting also has an RF transceiver 8 and memory 14, but is mains powered and has the control circuitry 20 to apply power to the light bulb 22. The light switch 2 is thus an example of a controller which has a control input 6 (the switch), whereas the light fitting is an example of a controlled device 4. The memory 14 in the controller includes a list 24 of device types that the controller can control, and control functions appertaining to the device types. The memory 14 in both controlled 4 and controller 2 devices also contains code 26 for causing the control circuitry to carry out the methods that will be described in more detail below.

FIG. 2 shows a representation of the software that resides on each of the devices in memory 14. The control application 30 communicates with the HUCL Software Stack 32 when certain events occur.

In a similar way the HUCL Software Stack 32 communicates with the RF Software Stack 34, and the RF Software Stack 34 will communicate back to the HUCL Software Stack 32 when certain events occur e.g. on receipt of data.

Messages 36 are sent and received. The messages may be of a number of types, including a simple device description query message, or any of a number of other message types.

The memory 14 of the light fitting 4 contains a precompressed simple device description message which can be simply sent out when a query is received requesting a simple device description from the light fitting 4. The control application in the light fitting is able to recognise such incoming simple device description query messages received from the transceiver 8 without decompressing them. This is possible because of the use of token-compression to compress the messages transmitted.

The operation of the devices will now be described with reference to FIG. 3. The first phase in the operation of this pair of devices is for the switch 2 (the controller) to discover the address of the light fitting 4 (the controlled device). This is known as device discovery, and it is a requirement of the underlying RF transport stack that device discovery is either provided (in the RF Software Stack), or that it is possible to implement device discovery on top of the transport stack (in the lower layer of the HUCL Software Stack).

The discovery process is initiated 100 by the Control Application in the controller (possibly as a result of some user interaction) by performing a call into the HUCL Software Stack requesting firstly the number of known devices, and then the network addresses of those devices. These device addresses are returned.

Depending on the underlying RF protocol, the network addresses may be established in some other way.

The end result of the device discovery phase is that the Control Application is supplied 102 with a list of addresses of all devices known by the RF Stack. At this point in the process the Control Application knows nothing more about each other device other than its address.

The second phase in the pairing process is for the Control Application to gather information on the devices for which it has addresses. This information is called the device description. The control application does this by making a call into the HUCL Software Stack, passing the address of the device that it requires the device description from.

The request for the simple device description is then passed 104 over the RF link to the destination device, so in the switch/fitting example described above the request is transmitted from the switch to the fitting. On receiving the request, the HUCL Software Stack at the destination device makes a call in to the Control Application requesting the device description. The format of the description is defined. If not already in a compressed form the description is compressed before being transmitted back to the sender of the request.

When the HUCL Software Stack on the requesting device receives 106 the device description, it is passed up to the Control Application. At this point the application has some basic information about the device and can make the decision as to whether it wished to communicate further with this device.

A design goal of HUCL is that it is suitable to operate on very simple devices, however the information necessary to fully describing a device is potentially quite complex. The list below shows the sort of information a device might want to provide as part of its description.

Device Type e.g. DVD

Vendor Name e.g. Philips

Model Number e.g. DVD1010/002

Serial Number e.g. AH06848032345

Vendor URL e.g. www.philips.com

For the simplest of control devices, such as the switch used in the example throughout this section, much of this information is probably redundant. It would however be of use on a higher end ‘PDA’ type remote control that has a screen where such information could be displayed to the user.

The processing of such descriptions on low-end devices such as light fitting 4 can present a problem, since it would potentially need the storage (RAM) to cache the complete message as it was received. The problem is worse than it might at first seem, since the overall size of the description data shown above is indeterminate, much of the information is ‘free text’; the vendor name could be very long, the URL could specify an exact page maybe even with parameters

e.g. http://www.consumer.philips.com/global/b2c/ce/catalog/subcategory.jhtml?gro upId=VIDEO&divId=0&catId=DVD&subCatId=DVDPLAYER

The way in which this is overcome in HUCL is that the device 30 description is split into two tiers of information. The first tier is a simplistic description of the device but identifying if further information is available. It does not contain any free text fields so the overall length of it is deterministic. The second tier of extended information is optional but provides additional information.

Referring to FIG. 9, the Simple Device Description message 230 includes as fields the device type 232, a field 238 to indicate if Extended Device Description available and other fields 236 identifying key information e.g. a flag to indicate if event subscription is available. Optional integer field 234 represents the number of sub-devices of a composite device. The skilled person will appreciate that the message 230 may also include a header and footer which are omitted for simplicity. The message will include compressed XML tokens which are likewise omitted for clarity. The fields of the Simple Device Description are all of fixed length, so that they can be dealt with readily without decompression.

After receiving 106 (FIG. 3) the Simple Device Description 230 the Simple Device Description 230 is passed back to the HUCL Stack.

In the present example, the light fitting 4 does not have an extended device description available and this is indicated by a flag in the simple device description 230.

If, however, another device is polled for which an Extended Device Description is available and the controller device requires it, the controller device Control Application may issue a “GetExtendedDescription” request 108 back to the device.

The HUCL Stack on the device receiving this request makes a Get Extended Description call into the Control Application requesting the Extended Device Description.

The Extended Device Description is passed back to the HUCL Stack, and makes its way back to the Control Application on the device that requested it. The Extended Description is then returned 110 to the requesting device.

If a GetExtendedDescription query is received on a device that does not provide an Extended Device Description the request is simply ignored.

Returning again to the switch/fitting example used throughout this section, from the point when the switch knows only the address of the fitting, the switch requests from the fitting its Simple Device Description. On receiving this it provides sufficient information such that the switch knows that it is talking to a light fitting that conforms to the standard fitting command set, it also knows that the light fitting 4 can't provide any Extended Device Description.

It is mandatory for a device application to provide a Simple Device Description to the HUCL Stack when requested. A device that does not provide any Extended Device Description can ignore any requests it receives for such information.

Included in the Simple Device Description returned by a device (when requested) is the device type field 232 that identifies the type of the device, e.g. TV, DVD, Light Fitting etc. The Device Type field 232 will identify to the controller (requesting the Simple Device Description) the instruction set that the device conforms to. HUCL devices identify themselves simply by their type identifier, they do not then go on to send messages to describe how they are controlled; there is no ‘runtime’ service description concept in HUCL. If a device identifies itself as a light fitting then the command set that can be called on this device is identified in the HUCL specification for a Light Fitting type device.

Referring to FIG. 4, all device types depend from a base device type 50. Top level elements 58 include in this example the controller device type 52, a basic device type 54 for controlled devices and an alarm device type 56.

Subsidiary device types 68 depend from the basic device type. In the example, these include a TV device type 64, a dimmable light device type 62 and a PVR device 60.

The Device Type Classification was to produce a system aims to allow a simple controller to identify whether it could control a device to the extent of the controllers' capabilities.

A simple switch could be paired with a light fitting to turn on and off a light, but one might argue that the control functionality of the switch, that is its ability to turn a device on or off should be applicable to any device than can accept an on/off concept e.g. a TV, Heater, Printer.

One way in which this could be implemented is for the switch to have a list of all of the devices it knows how to control (turn On or Off), so when it requests the Simple Device Description for a device, it can look at the Device Type field in the returned description and determine if it is within its list of device types it knows how to control.

There are two significant drawbacks of this approach. Firstly the switch is a very simple device and it is undesirable for the application within it to have to hold a list of all possible devices that it could control, which would be quite large; secondly if a new type of device is created after the switch is produced (which can accept simple On Off functionality), then the switch will not have this new device type in its list, and will not believe it can control it i.e. it is not extensible.

HUCL classifies devices in a hierarchical way, shown in FIG. 4. The Device Type field 232 (FIG. 9) identifies the device within the hierarchy and SO even if new devices were created, as long as it is derived from an the appropriate point within the hierarchy, a simple switch would still know that it could control it to an extent.

Devices that fall lower in the tree inherit the functionality of device types above it. It may be necessary to add some interpretation to the commands when applied to lower devices in the tree, for example the On/Off command when sent to a light will fairly obviously turn it On and Off, but the same commands when sent to a TV would place it in and out of standby mode.

The key benefit of the Device Type description is that even if the controller has no knowledge of the specific device type itself, it can determine the device from which it is derived, of which it may have some knowledge and hence may be able to control the device to some lesser extent (from the perspective of the device).

For example, consider the case that a light switch obtains the address of a device, it requests from this device the Simple Device Description; the Device Type field identifies the device as TV, but the switch does not recognise this as a device it knows about. However the switch can also establish from the description that it is a derivative of the ‘Basic Device’, which it does know about. The net result is that the switch can control the TV, to the extent of the controllers capabilities i.e. On and Off, despite knowing nothing about the device itself. The device could be a brand new category of device called an ‘XYZ’ invented long after the switch was manufactured, but so long as it is derived from a Basic Device the switch can still control it to an extent.

Although the Device Type Hierarchy may have just two tiers, and controller and basic device top level elements, at least one further tier and/or top level element is desirable. This caters for devices that would not comply with the functionality shown above in the Basic Device that is devices that do not have basic ‘Turn On’ ‘Turn Off’ functionality, e.g. an alarm. For illustrative purposes an ‘Alarm’ type device 56 has been shown in FIG. 4 and understandably this ‘Alarm’ device does not want to implement the normal On/Off functions that devices that are derived from Basic Device must have; it therefore sits at the same top level 58 in the hierarchy as the Basic Device 54 itself.

A second extension to the hierarchy is also shown in FIG. 4 i.e. the Enhanced TV Device 66 below the normal TV Device 64. Here the Enhanced TV Device inherits all of the functionality of both the Basic Device 54 and the TV Device 64, but also includes some extended functionality that is not present in a normal TV. A regular TV remote control designed to operate a normal TV Device can operate the Enhanced TV Device to the level of a normal TV Device functionality, but can't control the extended functionality.

The HUCL protocol accordingly provides an extensible mechanism for describing the Device Type and the devices above it from which it inherits functionality. Whilst the idea of a hierarchy of many layers might seem appealing, extending it beyond three or four levels will start to impact the size of the Simple Device Description.

Within HUCL it is possible to request a device description from a controller as well as a controllable device. When one device sends the “Get Simple Description” to a controller device (e.g. a switch) it is returned a Simple Device Description that contains a Device Type of “Controller”. The controller device may also make available an Extended Device Description which provides further information such as the manufacturer, model number etc.

It is important to note that the Device Type returned by a controller device is simply “Controller” 52 there is no hierarchy of different controller type devices defined in the device type tree. The reason for this is again trying to keep the protocol and messages sizes small and simple. It might be felt that it would be possible to have different controller types derived from the basic Controller such as a Switch, TV Remote Control, PVR Remote Control, etc. However a problem would occur with intelligent controllers such as Universal Remote Controller that are capable of controlling a wide range of devices. To include all of the possible controller types in a simple device description would result in a potentially large message, which goes against the ideal of trying to make the initial Simple Device Description simple. To determine the exact capabilities of a controller device different mechanisms are employed.

The first means of determining the capabilities of a controller device is by the Extended Device Description which is permitted on a controller device and may contain information such as the device name e.g. “Universal Remote Control” and whilst this is textual information and is not directly interpretable by application software, it can be presented to the user to assist in making an informed choice about a controller.

The second means for a device to determine more about a controller is by querying it.

The use of querying is a powerful mechanism for drip-feeding information about a device that would otherwise, if supplied en-mass, overload the requestor.

Each device of controller type provides a means for other devices to query 120 whether it is able to control a specific Device Type (FIG. 5). The device type passed in the query is the same field as is used in the Simple Device Description i.e. as defined in the Device Type Hierarchy. The controller returns 122 the level to which it can control the device, by returning the lowest device type in a list stored in the controller memory 14 that is the device type passed in the query or from which that device type depends. For example, a simple switch is queried whether it can control an Enhanced TV Device. Based on the hierarchy illustrated in FIG. 4 above the reply is that it can control it to the level of Basic Device. The switch would typically itself know nothing about a device type of Enhanced TV Device, but since the Device Type also includes the inherited devices it would be able to identify the Basic Device and return this as the lowest hierarchically superior device type it is capable of controlling.

The controller also implements an algorithm to determine if the switch can control a device type that is returned to it in a Simple Device Description (FIG. 6). When a switch discovers the address of a device it asks 124 the device for its simple device description, on receiving this information 126 the switch tests 128 whether it can control a device of this type to any degree, which is the same question it needs to respond to as a result of the querying process 120. The result is that the two query processes 120, 122, 124, 126, 128 do not add too much to the complexity of the simple switch device. The same applies to other simple devices.

It might be felt that the use of XML and its compression and de-compression on the simplest of devices is a little heavyweight. The use of XML to describe the protocol provides a solution that is easily extensible for future enhancements, relatively simple to describe and understand, can easily handle structured information and is instantly compatible with the ‘internet domain’.

Using a tagged compression technique on the XML (defined within HUCL) takes the relatively verbose protocol back down in size towards that of a traditional pure binary-based protocol, with some additional overhead to retain the content structure.

If one were to be presented with the a command in its compressed form it can be read in a similar manner that one would read any other binary based protocol, using information on the command structure and a table of definitions for data values. The only hint that the binary data may have originated from an XML based notation would be the presence of data to represent structure.

The HUCL specification defines that the messages is always transmitted through the transport medium in its compressed form. However on a simple device the application may operate directly on compressed messages, so eliminating the need on that device for the presence of the compression/de-compression software within the HUCL Software Stack. In this case the application would store (as part of the application image in ROM) the simple device description in its pre-compressed form, it would have a parser for the compressed protocol messages that it receives which would be similar in nature to any other binary protocol parser; any response messages would also need to be stored in their compressed form.

Using this approach the simplest devices such as the light switch and light fitting example used throughout this section can be implemented with a reduced software stack, and given that the number of commands that a simple device would need to understand and send is relatively small (turn light on, turn light off, toggle, get current state, get device description etc.) the overhead on the application software is minimal.

This offers a scalable solution to devices, where it is practical to implement the application to operate on compressed data this can be done, but when the device becomes more complex there will be a point where it becomes easier to include the compression/de-compression functionality in the stack and have the application use the protocol messages in their full XML notation. This cut off point is entirely down to the device designer and not defined or dictated by HUCL at all.

FIG. 7 illustrates how the components that make up HUCL fit together. It will be appreciated that the components are software components recorded in memory.

The following sections discuss in more detail the layers that form the HUCL software stack 32 and the functionality that they provide.

As has been stated earlier HUCL does not rely on a specific transport protocol (unlike for example TCP/IP) but instead sits directly on top of a transport stack 34. Different transport stacks 34 will by their nature offer differing services to applications and through differing API's; the HUCL Transport Adaption Layer 180 acts as a buffer to the specific transport layer.

The Transport Adaption Layer 180 provides to the higher layers in the HUCL stack a consistent transport independent set of services. The requirements of this layer are defined in detail in the Protocol Specification.

The messaging layer 182 provides the bulk of the functionality of the HUCL Software Stack. Applications communicate with this layer through the HUCL API and it will perform the calls back in to the application when necessary (e.g. when data is received).

The messaging layer 182 also handles any initial error reporting and if necessary acknowledgements. Message ID's and Transaction ID's used to check for missing messages and for coupling messages to replies are also handled fully by this layer.

The Messaging layer 182 also makes use of the Compression/Decompression services 184 as and when a message needs to be compressed or decompressed. As discussed earlier an application deals exclusively with messages in their compressed form, no calls are made to these services and they can be removed from the runtime stack.

Quite simply the compression and decompression services provide the message layer with the means to convert the HUCL messages between their compressed and decompressed forms. It is possible for this component of the system to be absent in low-end devices where all data exchanges with the application are made with compressed messages.

The application programming interface API 186 is the interface through which all applications communicate with the HUCL software Stack. Communication is bi-directional in that the HUCL stack will make asynchronous calls back to the application as a result of certain events occurring in the lower layers e.g. message received via the transport stack.

HUCL is transport stack 34 independent, and what this means is that the HUCL messaging protocol can be built on top of a variety of transport stacks, both wired and wireless.

Since HUCL is designed as a lightweight protocol it is therefore most suited to lightweight transport stacks as well such as the emerging Zigbee (802.15.4) standard, but it can sit equally well on top of TCP & UDP/IP which opens up a wide range of other protocols, both wired (e.g. Ethernet) and wireless (e.g. 802.11b).

For a HUCL to be implemented on a transport stack 34 it must be possible to provide a number of services to the messaging layer of the HUCL stack. This means that these services can either be present in the transport stack itself or it must be possible to implement any missing services in the Transport Abstraction Layer of the HUCL stack. These services may cover aspects such as addressing, message delivery and device discovery (e.g. discovering the addresses of other devices on the network).

The protocol itself is a document recorded on a medium 214, including the following information as shown in FIG. 8:

a generic HUCL message format 200 that defines the format to which all HUCL messages conform;

message definitions 202 defining the specific messages that form the control protocol.

message sequencing requirements 204 defining which messages are sent when, and the requirements of the application on receiving a message.

the HUCL API definition 206 defining the bi directional interface between HUCL and the application using it;.

the messaging System requirements and functionality 208 of the HUCL software stack;

a compression algorithm 210 defining the mechanism for the compression of the HUCL messages, and

a transport Adaption Layer definition 212 defining how the HUCL software stack is interfaced to a transport system (e.g. an RF stack). HUCL is accordingly not simply a message format definition but also encapsulates a message interchange and compression. The later four items in the list above form the HUCL software stack that would be present in a device, the first three items define the requirements to which the stack and application must conform.

From reading the present disclosure, other variations and modifications will be apparent to persons skilled in the art. Such variations and modifications may involve equivalent and other features which are already known in the design, manufacture and use of networks and which may be used in addition to or instead of features described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of disclosure also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to any such features and/or combinations of such features during the prosecution of the present application or of any further applications derived therefrom.

In particular, the specific subroutine names used in the examples may readily be varied. The computer program controlling the devices is shown as being recorded in memory 14 but the skilled person will realise that it could be recorded on many other types of record carrier such as a CD, floppy disc, etc.

Further, it will be noted that a very simple example of a light fitting and light switch has been extensively described in the forgoing. The skilled person will appreciate that many more complex control scenarios are also possible. 

1. A method of operating a networked device, including: receiving token-compressed messages; recognising in the received token-compressed messages incoming simple device description query messages requiring a simple device description response from the networked device, without decompressing the incoming messages; and sending a simple device description message (230) including a device type as a response to an incoming device query message requiring a simple device description response.
 2. A method according to claim 1, wherein the step of sending a simple device description includes reading a predetermined simple device description from a memory (14) in the networked device and sending the predetermined simple device description.
 3. A method according to claim 1 or 2 wherein the networked device is part of a wireless network and the steps of receiving token-compressed messages and sending the simple device description use wireless signals.
 4. A networked device, comprising a transceiver (8) for sending and receiving token-compressed human readable messages; and a message handler (26, 182) arranged to carry out the steps on incoming token-compressed human readable messages of: recognising received device query messages requiring a simple device description response from the networked device, without decompressing the incoming messages; and sending through the transceiver a simple device description including a device type as a response to an incoming device query message requiring a simple device description response.
 5. A networked device according to claim 4 further comprising a memory (14) storing a predetermined simple device description message precompressed from human readable format, wherein the message handler is arranged to read the predetermined simple device description message from the memory and send it through the transceiver in response to an incoming device query message.
 6. A system, comprising: a plurality of networked devices (2,4) each having a transceiver (8) for sending and receiving network messages; at least one networked device (2) arranged to send a simple device query message to other devices and to receive and interpret simple device description messages subsequently received from the other devices; each of the networked devices (2,4) being arranged to respond to an incoming simple device query message from another of the devices by sending a simple device description message (230) of defined length including a device type value representing the type of the device; and wherein the plurality of networked devices include at least one simple device (4) without the capability to decompress messages and interpreting directly compressed messages and at least one complex device including a message decompression arrangement (184) for decompressing the messages and a message interpreter for interpreting the decompressed messages.
 7. A system according to claim 6 wherein the or each simple device (4) further includes a memory storing a predetermined simple device description message precompressed from human readable format, wherein the message handler is arranged to read the predetermined simple device description message from the memory and send it through the transceiver in response to an incoming device query message.
 8. A system according to claim 6 or 7 wherein the networked devices include at lest one device includes a message decompression unit arranged to decode messages and to act on the decoded messages.
 9. A computer program product, comprising code for receiving token-compressed messages; code for recognising in the received token-compressed messages incoming simple device description query messages requiring a simple device description response from the networked device, without decompressing the incoming messages; and code for sending a simple device description (230) including a device type as a response to an incoming device query message requiring a simple. device description response. 